1. Field of the Invention
The present invention relates to a sensor device with an improved method for setting a threshold value.
2. Description of the Prior Art
Conventionally, sensor devices are known that are capable of detecting the presence or absence of bodies, etc. They detect the presence or absence of a body, etc. by comparing a detection signal, outputted according to the detection state of an object, with a predetermined threshold value.
Such sensor devices are configured to allow changes in the settings, such as threshold values. As a setting change device, for example, some sensor devices are equipped with multiple buttons for use in changing the settings. Pressing the buttons can change a threshold displayed on a digital indicator. This allows an operator to accurately set the threshold value while looking at the digital indicator.
For example, as disclosed in Japanese Utility Model No. 4-76003, there is a sensor device that is equipped with a rotatable input element, such as a variable resistor. This element allows the operator to change a setting by rotating the variable resistor to a desired position while looking at a graduated scale. The rotatable input element makes it possible to set a threshold value through a simpler operation than the pushing of buttons.
Generally, sensor devices allow the operator to set not only the threshold value, which is the detection sensitivity, but also various values related to other various functions, including the timing and output duration of a signal outputted from the sensor device and the light-emission period of a photoelectric sensor. With a type of sensor in which settings are changed by pressing buttons, settings are made in each of these various functions by switching among the operation modes of the buttons. This makes it difficult for an operator to see at a glance how to change a desired setting, causing the inconvenience of having to operate the buttons while keeping an operations manual at hand.
Also, to change a threshold by 10 steps for example, a setting button must be pressed 10 times. This is troublesome. Generally, the operator tends to press a button faster corresponding to increases in the total number of times he/she must press the button. Consequently, the operator may often press a button for an incorrect number of times. If, for example, the button is mistakenly pressed for an additional 10 times, the threshold value is changed too much and must be returned to a predetermined value (in this case corresponding to 10 more button pressings). This complicates the task of setting the threshold value.
On the other hand, it is easy to understand the operating method (setting method) when changing a setting by rotating a variable resistor to a specific scale position. However, it is difficult to make an accurate setting because the visually determined scale position (setting) has an unavoidable difference from the actual setting.
The present invention has been made in view of the above circumstances and has as an object to provide a sensor device that allows settings to be accurately changed through relatively simple operations.